With the development of electronics in recent years, demands for semiconductors for forming memories, integrated circuits, etc. are rapidly increasing. Those semiconductors are manufactured such that impurities are doped into a semiconductor substrate with an extremely high purity to impart electrical properties thereto, or semiconductor substrates with minute circuit patterns formed thereon are laminated. Those manufacturing steps must be performed in a chamber with a high vacuum state so as to avoid influences of dust etc. in the air. This chamber is generally evacuated by using a vacuum pump as a pumping system. In particular, a turbo molecular pump, which is one of the vacuum pumps, is widely used since the turbo molecular pump entails little residual gas, is easy of maintenance, and has other such characteristics.
The semiconductor manufacturing process includes a number of steps in which various process gases are caused to act onto a semiconductor substrate, and the turbo molecular pump is used not only to evacuate the chamber but also to discharge those process gases from the chamber. Further, in equipment for an electron microscope etc., the turbo molecular pump is used to create a high vacuum state in the chamber of the electron microscope etc. in order to prevent refraction etc. of an electron beam caused by the presence of dust or the like.
Such the turbo molecular pump is composed of a turbo molecular pump main body for sucking and discharging gas from the chamber of a semiconductor manufacturing apparatus, an electron microscope, or the like, and a control device for controlling the turbo molecular pump main body. FIG. 10 is a vertical sectional view of the turbo molecular pump main body.
In FIG. 10, a turbo molecular pump main body 100 includes an outer cylinder 127 with an inlet port 101 formed on the top thereof. Provided inside the outer cylinder 127 is a rotor 103 having in its periphery a plurality of rotary vanes 102a, 102b, 102c, . . . serving as turbine blades for sucking and discharging gas, formed radially in a number of stages. At the center of the rotor 103, a rotor shaft 113 is mounted while being supported in a levitating state in the air and controlled in position, for example, by a 5-axis control magnetic bearing.
Upper radial electromagnets 104 are provided by arranging four electromagnets in pairs in X- and Y-axis and plus- and minus-side directions (not shown.; those electromagnets are denoted by 104X+, 104X−, 104Y+, and 104Y−, as necessary). Further, there is provided an upper radial sensor 107 constituted of four electromagnets arranged in close proximity to and in correspondence with the upper radial electromagnets 104. The upper radial sensor 107 detects radial displacement of the rotor 103, transmitting a signal to a control device (not shown).
In this control device, the upper radial electromagnets 104 are controlled through excitation by an amplifier circuit 150 (to be described later), through a compensation circuit having a PID adjusting function, on the basis of a displacement signal detected by the upper radial sensor 107, which adjusts the radial position of the upper portion of the rotor shaft 113.
The rotor shaft 113 is formed of a high-magnetic-permeability material (e.g., iron) and is adapted to be attracted by the magnetic force of the upper radial electromagnets 104. Such adjustment is conducted independently in the X-axis direction and the Y-axis direction.
Further, lower radial electromagnets 105 and a lower radial sensor 108 are arranged in the same way as the upper radial electromagnets 104 and the upper radial sensor 107. Like the radial position of the upper portion of the rotor shaft 113, the radial position of the lower portion of the rotor shaft 113 is adjusted (the lower radial electromagnets 105 are similarly denoted by 105X+, 105X−, 105Y+, and 105Y−, as necessary).
Further, axial electromagnets 106A and 106B are arranged on the upper and lower sides of a circular metal disc 111 provided in the lower portion of the rotor shaft 113. The metal disc 111 is formed of a high-magnetic-permeability material such as iron. To detect axial displacement of the rotor shaft 113, an axial sensor 109 is provided, which transmits an axial displacement signal thereof to the control device.
The axial electromagnets 106A and 106B are controlled through excitation by the amplifier circuit 150, through the compensation circuit having a PID adjusting function of the control device on the basis of the axial displacement signal. The axial electromagnet 106A upwardly attracts the magnetic disc 111 by the magnetic force, and the axial electromagnet 106B downwardly attracts the magnetic disc 111.
In this way, the control device has a function to appropriately control the magnetic force exerted on the metal disc 111 by the axial electromagnets 106A and 106B, magnetically levitate the rotor shaft 113 in the axial direction, and retain the rotor shaft 113 in the space in a non-contact state.
Note that descriptions will be given later in more detail on the amplifier circuit 150 that drives, through excitation, the upper radial electromagnets 104, the lower radial electromagnets 105, and the axial electromagnets 106A and 106B.
Meanwhile, a motor 121 is equipped with a plurality of magnetic poles, which are arranged circumferentially to surround the rotor shaft 113. The magnetic poles are respectively controlled by the control device to rotate the rotor shaft 113 through an electromagnetic force acting between the rotor shaft 113 and the magnetic poles.
In addition, the motor 121 also has an RPM sensor (not shown) incorporated to output a detection signal, which is used for detection of RPM of the rotor shaft 113. A phase sensor (not shown) is attached, for example, in the vicinity of the lower radial sensor 108 to detect the phase of rotation of the rotor shaft 113. From detection signals of the phase sensor and the RPM sensor both, the control device detects positions of the magnetic poles.
A plurality of stationary vanes 123a, 123b, 123c, . . . are arranged so as to be spaced apart from the rotary vanes 102a, 102b, 102c, . . . by small gaps. To downwardly transfer the molecules of exhaust gas through collision, the rotary vanes 102a, 102b, 102c, . . . are inclined by a predetermined angle with respect to a plane perpendicular to the axis of the rotor shaft 113. Similarly, the stationary vanes 123 are also inclined by a predetermined angle with respect to a plane perpendicular to the axis of the rotor shaft 113, and extend toward the inner side of the outer cylinder 127 to be arranged alternately with the rotary vanes 102.
The stationary vanes 123 are supported at one end by being inserted into gaps between a plurality of stationary vane spacers 125a, 125b, 125c, . . . stacked together in stages. The stationary vane spacers 125 are ring-shaped members, which are formed of a metal, such as aluminum, iron, stainless steel, or copper, or a metal such as an alloy containing such the metal as a component.
In the outer periphery of the stationary vane spacers 125, the outer cylinder 127 is secured in position with a small gap therebetween. At the bottom of the outer cylinder 127, there is arranged a base portion 129, and a threaded spacer 131 is arranged between the lower portion of the stationary vane spacers 125 and the base portion 129. In the portion of the base portion 129 below the threaded spacer 131, there is formed a exhaust port 133 which communicates with the outside.
The threaded spacer 131 is a cylindrical member formed of a metal, such as aluminum, copper, stainless steel, or iron, or a metal such as an alloy containing such the metal as a component, and has a plurality of spiral thread grooves 131a in its inner peripheral surface. The spiral direction of the thread grooves 131a is determined such that when the molecules of the exhaust gas move in the rotating direction of the rotor 103, these molecules are transferred toward the exhaust port 133.
Connected to the lowermost one of the rotary vanes 102a, 102b, 102c, . . . of the rotor 103 is a rotary vane 102d, which extends vertically downwards. The outer peripheral surface of the rotary vane 102d in a cylindrical shape sticks out toward the inner peripheral surface of the threaded spacer 131, and is in close proximity to the inner peripheral surface of the threaded spacer 131 with a predetermined gap therebetween.
The base portion 129 is a disc-like member constituting the base of the turbo molecular pump main body 100, and is generally formed of a metal, such as iron, aluminum, or stainless steel. The base portion 129 physically retains the turbo molecular pump main body 100, and also functions as a heat conduction passage. Thus, the base portion 129 is desirably formed of a metal that is rigid and high in heat conductivity, such as iron, aluminum, or copper.
In the above-mentioned construction, when the rotary vanes 102 are driven by the motor 121 to be rotated together with the rotor shaft 113, an exhaust gas from a chamber is sucked in through the inlet port 101 by the action of the rotary vanes 102 and the stationary vanes 123.
The exhaust gas sucked in through the inlet port 101 passes between the rotary vanes 102 and the stationary vanes 123, and is transferred to the base portion 129. At this time, the temperature of the rotary vanes 102 is raised by frictional heat generated when the exhaust gas comes into contact with the rotary vanes 102 and by heat generated and conducted from the motor 121. Such the heat is transferred to the stationary vanes 123 through radiation or through conduction of gas molecules of exhaust gas or the like.
The stationary vane spacers 125 are joined to one another on the outer periphery and transmit, to the outside, heat received by the stationary vanes 123 from the rotary vanes 102 as well as frictional heat generated upon contact between exhaust gas and the stationary vanes 123. The exhaust gas transferred to the base portion 129 is sent to the exhaust port 133 while being guided by the thread grooves 131a of the threaded spacer 131.
Herein, the turbo molecular pump requires control based on individually adjusted specific parameters (e.g., identification of the model and characteristics corresponding to the model). To store the control parameters, the turbo molecular pump main body 100 contains an electronic circuit portion 141 in its main body. The electronic circuit portion 141 is composed of a semiconductor memory, such as EEP-ROM, electronic parts, such as semiconductor devices for access to the semiconductor memory, a substrate 143 for mounting these components thereto, etc. This electronic circuit portion 141 is accommodated under an RPM sensor (not shown) near the center of the base portion 129 constituting the lower portion of the turbo molecular pump main body 100, and is closed by a hermetic bottom cover 145.
Given next is a detailed description of the amplifier circuit for driving, through excitation, the upper radial electromagnets 104, the lower radial electromagnets 105, and the axial electromagnets 106A and 106B of the turbo molecular pump main body 100 structured as above. Patent Document 1 is known as a conventional example of the amplifier circuit.
FIG. 11 shows a diagram of a conventional amplifier circuit. Electromagnet coils 151, 151, . . . which respectively constitute the electromagnets 104, 105, 106A, and 106B are elements present on the turbo molecular pump main body 100 side. The electromagnet coils are shown for simplicity.
In FIG. 11, the electromagnet coil 151 is connected at one end 151a to a transistor 161 and a diode 165, while the electromagnet coil 151 is connected at the other end 151b to a transistor 162 and a diode 166 through an electromagnetic current detecting circuit 155.
Herein, the transistors 161 and 162 are both power MOSFETs. The transistor 161 has a drain terminal 161a connected to a positive electrode 153a of a power source 153 and has a source terminal 161b connected to the one end 151a of the electromagnet coil 151. The transistor 162 has a drain terminal 162a connected to the other end 151b of the electromagnet coil 151 through the electromagnetic current detecting circuit 155 and has a source terminal 162b connected to a negative electrode 153b of the power source 153.
In addition, the diodes 165 and 166 are both provided for current regeneration. The diode 165 has a cathode terminal 165a connected to the one end 151a of the electromagnet coil 151 and has an anode terminal 165b connected to the negative electrode 153b. Similarly, the diode 166 has a cathode terminal 166a connected to the positive electrode 153a and has an anode terminal 166b connected to the other end 151b of the electromagnet coil 151 through the electromagnetic current detecting circuit 155.
The electromagnetic current detecting circuit 155 connected to the other end 151b of the electromagnet coil 151 is, for example, a hole sensor type current sensor, and detects the amount of a current flowing in the electromagnet coil 151 (hereinafter referred to as “electromagnetic current iL”) to output an electromagnetic current detection signal 173 as the detection result to an amplifier control circuit 171 (to be described later) Also, provided between the positive electrode 153a and the negative electrode 153b of the power source 153 is a capacitor (not shown) for stabilizing the power source 153.
The amplifier circuit 150 configured as described above is provided for each of the electromagnet coils 151, 151, . . . which respectively constitute the electromagnets 104, 105, 106A, and 106B.
The amplifier control circuit 171 is a circuit within a digital signal processor portion (hereinafter referred to as “DSP portion”) (not shown) of the control device. The amplifier control circuit 171 compares the value of the electromagnetic current iL detected by the electromagnetic current detecting circuit 155 and a current command value. Based on the comparison result, the pulse width time of each of gate drive signals 174 and 175 to be outputted to the gate terminals of the transistors 161 and 162 is determined within a control cycle Ts, which is one cycle by PWM control.
In the above-mentioned structure, when the transistors 161 and 162 of the amplifier circuit 150 are both turned on, the electromagnetic current iL is increased due to a current supplied from the positive electrode 153a to the negative electrode 153b through the transistor 161, the electromagnet coil 151, and the transistor 162. On the other hand, when the transistors 161 and 162 are both turned off, the electromagnetic current iL is decreased due to a current regenerated from the negative electrode 153b to the positive electrode 153a through the diode 165, the electromagnet coil 151, and the diode 166.
In this case, when the value of the electromagnetic current iL detected by the electromagnetic current detecting circuit 155 is smaller than the current command value, control is performed such that the electromagnetic current iL is increased in the amplifier control circuit 171. Therefore, as shown in FIG. 12, in one control cycle Ts, the pulse width time during which the transistors 161 and 162 are both kept turned on is set to be longer than the pulse width time during which the transistors 161 and 162 are both kept turned off. As a result, the electromagnetic current iL in one control cycle Ts is increased since an increasing time Tp1 for the electromagnetic current iL is set to be longer than a decreasing time Tp2 for the electromagnetic current iL.
On the other hand, when the value of the electromagnetic current iL detected by the electromagnetic current detecting circuit 155 is larger than the current command value, control is performed such that the electromagnetic current iL is decreased in the amplifier control circuit 171. Therefore, as shown in FIG. 12, in one control cycle Ts, the pulse width time during which the transistors 161 and 162 are both kept turned off is set to be longer than the pulse width time during which the transistors 161 and 162 are both kept turned on. As a result, the electromagnetic current iL in one control cycle Ts is decreased since the decreasing time Tp2 for the electromagnetic current iL is set to be longer than the increasing time Tp1 for the electromagnetic current iL.
By the settings, the electromagnetic current iL in the control cycle Ts can be appropriately increased or decreased, so the value of the electromagnetic current iL and the current command value can be made to be the same.
Note that the detection of the electromagnetic current iL in the electromagnetic current detecting circuit 155 is performed once at the same detection timing Td in the control cycle Ts as shown in FIG. 12.
Patent Document 1: JP 3176584 B (FIG. 8 and FIG. 9)
As described above, the amplifier circuit 150 is provided for each of the electromagnet coils 151, 151, . . . which respectively constitute the electromagnets 104, 105, 106A, and 106B, so, in the case of a magnetic bearing in a five axis control, ten amplifier circuits 150 are provided in the control device. The respective amplifier circuits 150 are each constituted of a bridged circuit which is composed of two transistors 161 and 162 and two diodes 165 and 166 as shown in FIG. 11, so twenty transistors and twenty diodes are required for driving, through excitation, all the electromagnet coils 151, 151, . . . .
As a result, the amplifier circuit 150 is composed of a large number of elements, so it is difficult to reduce the size of the amplifier circuit 150, and it is also difficult to reduce the size of the entirety of the turbo molecular pump. In view of this, a large space is required when the turbo molecular pump is installed in the clean room or the like, so there is a fear of increasing the costs of installation. Also, there is a fear of increasing the failure rate because the number of elements constituting the amplifier circuit 150 is increased. In addition, there is a fear of increasing power consumption and heat generation within the amplifier circuit 150. Further, there is a fear of increasing the manufacturing costs or the like of the amplifier circuit 150 itself because of the increase in the number of the elements.
In addition, the electromagnet coil 151 is an element provided to the turbo molecular pump main body 100 side as shown in FIG. 11, so nodes at both ends 151a and 151b (these nodes are respectively referred to as “node R” and “node S”) of the electromagnet coil 151 are wirings constituting a cable between the control device and the turbo molecular pump main body 100. Considering that ten amplifier circuits 150 are provided in the control device, twenty wirings serving as nodes R and S are assumed to be provided in the cable between the control device and the turbo molecular pump main body 100. As a result, it is necessary to increase the number of cores for the cable between the control device and the turbo molecular pump main body 100, or it is necessary to increase the size of a connector (not shown) serving as a port of the cable at the turbo molecular pump main body 100 side, so there is a fear that the respective costs of parts are increased.
Further, in control of a conventional amplifier circuit 150, the electromagnetic current iL is always increased or decreased within the control cycle Ts (that is, not constant) as shown in FIG. 12. Thus, the electromagnetic current iL is in a transient state at a detection timing Td for detecting the electromagnetic current iL. In view of this, when only a small gap or the like is generated between the detection timing Td and a waveform of an actual electromagnetic current iL, there is a fear of generating a large error with respect to the value of the electromagnetic current iL that is intended to be detected. Further, when the increase and decrease of the electromagnetic current iL is switched in the vicinity of the detection timing Td, noise may be generated within the amplifier circuit 150, or noise may be allowed to overlap the positive electrode 153a and the negative electrode 153b of the power source 153, which leads to a fear of generating the detection error.